In the area of thermal printers, it is wellknown that the use of such printers is increasing for certain operations that require a reduction in noise levels and at a reasonable cost. While development work is continually progressing to increase the speed of operation with minimum maintenance or care of the equipment, it is seen that improvements are being made to provide a higher quality print with a reduced number of thermal elements.
In the case of thermal printers, it is necessary to minimize the complexity of the thermal print head and the associated electronic controls. In certain prior art printers, it has been common practice to provide a thermal print head having a plurality of thermal printing elements on the surface of the head and wherein selected elements are energized to provide printing on thermal paper or like record media with the print head operating in a stationary or fixed position relative to the printer frame. The thermal printing elements on the print head may take the form of pads or contact surfaces in the shape of characters and connected by conducting runs to side or edge connectors. A flexible flat ribbon-like cable is normally used to connect with the pads or contact surfaces on the print head and the individual leads or wires of the cable may include end connectors or terminals for contact with the print head pads.
More recently, development work in thermal printers has included a shuttling-type print head having approximately 20% of the number of print elements as compared to the number of elements on a fixed or stationary head.
One of the problems encountered with the shuttling print head is that of smudging the thermal paper on which the printed image is formed by reason of pressure or contact between the print head and the paper or between the print head and the platen during travel of the print head across the printer. Since it is common practice to print in one direction of travel of the print head, it is deemed to be an improvement over prior printing apparatus and is advantageous to eliminate or at least reduce the pressure of the print head against the thermal paper and against the platen during the return cycle of the print head and its carriage.
Representative prior art in the field of thermal print heads includes U.S. Pat. No. 3,509,980, issued to C. R. Loughry et al. on Mar. 12, 1968, which discloses a thermal printer having a print head slidably mounted on a guide bar member which pivots to force the print head into engagement with a thermally-sensitive print medium and such force is controlled by a spring.
U.S. Pat. No. 3,777,116, issued to R. Brescia on Dec. 4, 1973, discloses a thermographic print head which utilizes springs to hold the resistive elements in firm contact with a metal band.
U.S. Pat. No. 4,000,393, issued to M. J. Cochran et al. on Dec. 28, 1976, discloses a thermal print head assembly wherein the heating elements are typically held in contact with the thermally sensitive paper by a spring-loaded pivot arrangement.
U.S. Pat. No. 4,173,273, issued to T. Hanakata on Nov. 6, 1979, discloses a thermal printer device having an electromagnetic plunger to control printing and to urge the thermal head against the printing medium with a predetermined pressure force. A spring controls relative movement between the head and the medium with a lower pressure force.